As is well known in the prior art, a draft gear, in order to be installed into the sill of the freight car, must be in a partially compressed state. In service, the housing of the draft gear abuts the rear draft stops of the car structure while the wedge or friction parts press against the follower plate, which in turn abuts the front draft stops. This spring-loaded state is maintained by the draft gear's internal spring means. Since the space available between the front and rear draft stops is approximately one-quarter to three-eights inch less than the length of an ungagged draft gear and the follower plate combined, it is apparent that the draft gear must be precompressed and held in that state prior to positioning within the pocket.
To overcome this problem of preshortening, the railroad industry has for many years insisted that manufacturers of draft gears furnish the draft gear in a precompressed or gagged state. In this preshortened condition, the draft gear is at an over-all length which is approximately one-quarter to three-eights inch less than the length at which the gear would be when situated within the pocket in service. When in such a reduced length or compressed state, the draft gear and follower plate can easily be inserted between the draft stops. It is further an industry requirement that the preshortened draft gear, of its own accord, be able to self-extend and become tight in the draft pocket once service has begun. In essence, a draft gear manufacturer must provide a means by which his draft gear can be first precompressed, then held in that precompressed length for an indefinite period of time until the unit is put in service within a freight car, after which time the preshortening means must disengage. The preshortening requirements of the railroad industry have always presented a dilemma for the draft gear manufacturer. A preshortening device must be strong enough to hold a draft gear, some of which are designed to take shocks of up to 1,000,000 lbs., in a precompressed state while it is shipped, stored and otherwise handled. It must then be weak enough to be relatively disengageable when it is placed in actual service in the freight car. Should the preshortening insert be too weak, it can be triggered or fragmentated while handling, shipping or whatever; and should it be too strong, it will continue to maintain the draft gear in a gagged condition even after the railroad car is placed in a working environment. This results in increased coupler slack and additional distress to the draft stops as a result of the draft gear being loose within the pocket.
It has been the common practice with draft gears such as those shown in U.S. Pat. No. 3,227,288 to H. W. Mulcahy et al, dated Jan. 4, 1966, and U.S. Pat. No. 3,966,057 to Francis H. Duquette et al, dated June 29, 1976, to employ fragmentable preshortening inserts. These preshortening inserts, when subjected to external forces during a work cycle which exceed their yield point, fracture or disintegrate and thus release the draft gear from the compressed state. Often times these preshortening inserts are composed of powdered metal mixtures. For example, a preshortening insert has been employed in the draft gear identified above in U.S. Pat. No. 3,966,057 which is a powdered metal mixture and has a generally solid, generally cubic structure. Even though all of the edges of the generally cubic structure have been chamfered, it has been found that such preshortening inserts from time to time in service do not fragment and release the draft gear from the gagged state.